(4/4)
Hint: For the download and uploads you can also use our
Speed Test page
. Please ignore the values for download/upload speed from the Speed Test as long as cFosSpeed is not calibrated.

After the calibration, please start this Speed Guide again.

Can you calibrate cFosSpeed to 98% or above?

Yes
No

For the line calibration to work, cFosSpeed must receive Ping responses. Please check if "Pongs Received" in the adapter
info is at least 50%.
If it is less than 50%, please have a look at our troubleshooting page
no-ping.htm
, otherwise you can contact us by using the mail form below.
Contact us

Speed too low

When you install cFosSpeed for the first time it changes your TCP window size. For this to take effect, you need to reboot
your system.

Have you rebooted your machine?

Yes
No

Traffic Shaping may cost 1-2% speed. This is a necessary consequence of the speed regulation for Traffic Shaping.

Test
if the speed is also low with cFosSpeed uninstalled.

Is it still low?

Yes
No

Then it's no cFosSpeed problem. In most cases the server you connect to may have speed problems.

Test if the speed is also low with Traffic Shaping disabled.

Is it still low?

Yes
No

The cFosSpeed network driver may cause this problem. Is your computer fast enough for your connection? Otherwise we would
like to know about the problem.

Please send us an email, so we can have a closer look at your problemContact us

Check the Low Latency Mode setting

Low Latency Mode active?

Yes
No

Try to turn it off in the cFosSpeed console:

spd gset latency 2 -save

If this helps, please let us know your network configurationContact us

Make two speed tests: download and upload. Each for 2-3 Minutes.

Do you get the raw max. speed of your connection?

Yes
No

cFosSpeed can not increase the raw speed of your connection. It cannot make a 11Mbit/s connection out of a 10Mbit/s connection.
cFosSpeed can improve your Internet connection whenever you have several connections at the same time, like a long email
send and web-surfing, or filesharing and web-surfing.

Does the cFosSpeed prioritization work for you?

Yes
No

(1/6)
cFosSpeed tries to keep your ping low. cFosSpeed Traffic Shaping should result in max. bandwidth (especially with several
simultaneous connections) while having minimal ping times (in fact the ping time should be nearly the ping time you get when
not transferring data at all). There may be a trade-off between low ping time and transfer speed. If you can live with a
higher ping time, you can try this in the cFosSpeed Console:

For a higher upload speed:

spd set tx_delay
tx_delay =
10000

C:\Program Files\cFosSpeed>

spd set tx_width
tx_width =
1000

C:\Program Files\cFosSpeed>

Write down the two values.

(2/6)
Now double each of them and try the following:

spd set tx_delay
20000
tx_delay =
20000

C:\Program Files\cFosSpeed>

spd set tx_width
2000
tx_width =
2000

C:\Program Files\cFosSpeed>

(3/6)
If this doesn't help, restore the old values.

spd set tx_delay
10000
tx_delay =
10000

C:\Program Files\cFosSpeed>

spd set tx_width
1000
tx_width =
1000

C:\Program Files\cFosSpeed>

(4/6)For a higher download speed:

spd set rx_delay
rx_delay =
20000

C:\Program Files\cFosSpeed>

spd set rx_width
rx_width =
1970

C:\Program Files\cFosSpeed>

Write down the two values.

(5/6)
Now double each of them and try the following:

spd set rx_delay
40000
rx_delay =
40000

C:\Program Files\cFosSpeed>

spd set rx_width
3940
rx_width =
3940

C:\Program Files\cFosSpeed>

(6/6)
If this doesn't help, restore the old values.

spd set rx_delay
20000
rx_delay =
20000

C:\Program Files\cFosSpeed>

spd set rx_width
1970
rx_width =
1970

C:\Program Files\cFosSpeed>

Did this help?

Yes
No

There are (rare) cases when cFosSpeed RX shaping reduces the download speed.To solve this problem try the following
in the cFosSpeed Console:

spd gset rx_shape 0 -save

There are also (rare) cases where the packet loss of your connection confuses cFosSpeed's Traffic Shaping.To solve this
problem try the following in the cFosSpeed Console:

spd gset avoid_loss 0 -save

Did this help?

Yes
No

(1/2)
Sometimes the speed measurements drifts over time because there is always an extreme amount of connections and a lot of
UDP traffic. This can happen in some BitTorrent cases. Calibration works fine, but after a while the connections become slower
and slower.

Only in such cases you can set the speed to fixed:
Get the current values by using the cFosSpeed Console:

spd set maxtxacked
maxtxacked =
537274

C:\Program Files\cFosSpeed>

spd set maxtxraw
maxtxraw =
537916

C:\Program Files\cFosSpeed>

(2/2)
Now choose a value between these two numbers and take 90% to 98% of it (510715 in this
example).Set it with

spd set fixed 1; set txspeed
510715
fixed = 1
txspeed =
510715

C:\Program Files\cFosSpeed>

If your pings are getting too high, you can reduce this speed in 1% steps.

Pings too high

Is the Low latency Mode active?

Low latency Mode active?

Yes
No

Try to turn it on:

spd gset latency 1 -save

(1/2)
Maybe the high ping times are caused by the server at the other end of the connection. This often happens with game servers.
cFosSpeed cannot reduce your ping below the minimum which is determined by your connection / ISP. Whenever you use several
connections simultaneously cFosSpeed can reduce the ping time and prioritize your traffic so that you get near minimum ping
times while still using nearly all available bandwidth. This allow, for example, uploads / downloads during VoIP calls or
online gameplay.
Uninstall cFosSpeed or disable Traffic Shaping

(2/2)
Download
hrping
and - without any other traffic on your connection - try both

hrping www.cfos.de

hrping -u www.cfos.de

Is the ping time still high?

Yes
No

Tip: For DSL connections use fastpath. WLAN typically has higher ping times as cable based networks. Mobile Internet may
cause additional delay due to bad transfer conditions and/or congestion of the access point.

Is there another PC in the network which sends/receives data?

Are your ping times good if this PC doesn't use the internet?

Yes
No

You can limit this PC's transfer rate. Install cFosSpeed on it and if this doesn't help, limit this PC's upload speed:

spd set tx_limit [value]

Maybe there is something wrong with the prioritization? Please open "current connections" and check if each connection
has the bandwidth it should have.

Is the prioritization correct?

Is the ping time better now?

Yes
No

Some equipment interferes with TCP transmissions. For example some drivers for Atheros WLAN adapters may cause high pings
with downloads. Please install the most recent network drivers. For a test, use another network adapter and see if pings
times are still high during downloads.

New drivers / other network card helped?

Yes
No

Is your cFosSpeed set to fixed speeds? Check this by typing the following into the cFosSpeed Console:

spd set fixed
fixed =
0

C:\Program Files\cFosSpeed>

It should be 0, except for rare cases with a lot of BitTorrent connections and high UDP traffic.

If your cFosSpeed line calibration remains stable, you should set it to 0:

spd set fixed 0

or use smaller values for the fixed speed (try reducing the speed in 1% steps).

Prioritization

(1/2)
Prioritization can only work, if not all data is prioritized. It works best if only a little of the traffic is prioritized
high and the rest normal. cFosSpeed sends out all packets as fast as possible. But (only) when there traffic with different
priorities then higher prioritized packets are sent first. This is how you can test whether the prioritization scheme works:
Clear the current statistics

The traffic in all classes above "default" should be no more than 20%-40%.

Is it more than 20%-40%?

Yes
No

(1/2)
See which connections consume bandwidth. Transfer data for a time and look at the current connections

(2/2)
Is the protocol or program you want to prioritize set to "high" or "higher" and everything else to "normal" or lower? If
not, open the prioritize protocol or program dialog (under "Options > Settings") and adjust the settings. You can also add
a program, if it is missing.

Did this help?

Yes
No

Connection problems

Please check, if "Automatic MSS (MTU) optimization" is activated:
Some servers rely on a maximum MSS/MTU, so you can try to turn it off.

Also check if "Net Talk" is activated. You
could try if it helps to turn it off.

(5/5)
You may also try "Automatic MSS (MTU) optimization".
In many cases a slightly lower MSS/MTU gains a few % of transfer speed. But some servers rely on a maximum MSS/MTU, so turn
off "Automatic MSS (MTU) optimization" if you experience problems

How to check whether you benefit from cFosSpeed Traffic Shaping

cFosSpeed cannot increase the raw speed of your Internet connection. Also it cannot reduce your ping time below the minimum
ping of your Internet connection. So you can only measure the benefits of Traffic Shaping during active data transfer which
uses up your available bandwidth.

Upload at full speed for 1-2 minutes

Download at full speed for 1-2 minutes

Do a combined upload and download at full speed

During all 3 scenarios, use
hrping
in the
cFosSpeed Console
to measure your ping.

hrping -t -u www.cfos.de

Now try all 3 scenarios with and without Traffic Shaping
In all scenarios you should see a lower ping time with Traffic Shaping enabled. In scenario 3 you may also experience a
higher download speed. The upload speed may be slightly reduced, because cFosSpeed needs the upload bandwidth to send the
ACKs for the download fast enough.

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